I have a 2-year-old Dell system with an i5-2400 processor (system cost $600 when new).
I use a $120 nVidia GTX 750 Ti graphics card.
With the default graphics settings in AH beta (includes anti-aliasing turned on, 4096 texture size, 1920x1080 screen size), I get 55-60 fps while flying around among the dones circling the A1 airfield on the default map.
You can buy a better system from Dell today for $550 (the Dell Inspiron Desktop with an i5-4460 processor). Add $50 for a beefier power supply, plus whatever you want to pay for a graphics card ($150 will get you a card faster than my GTX 750 Ti), and you have a machine faster than the above.